1. Field of the Invention
This invention relates to a battery pack which integrates the charging or discharging current generated when fed to an apparatus or charged by a charger, and then, calculates the remaining capacitance in accordance with the result of the integration.
2. Related Background Art
As a battery pack of the kind, there has been known the one disclosed in Japanese Utility Model Application Laid-open No. 4-44632. In conjunction with FIG. 1 to FIG. 3 which represent an embodiment of this invention, the description will be made of such a battery pack. FIG. 1 which illustrates a battery pack according to this invention corresponds to FIG. 3 of the above-mentioned Laid-Open Application. Likewise, FIG. 2 corresponds to FIG. 10, and FIG. 3 to FIG. 11. The AC power supplied through an AC plug 1 shown in FIG. 3 is converted to a direct current in a charging circuit 2, and supplied to a secondary battery pack 4 through terminals 3A and 3B. The terminals 3A and 3B are provided for the charging plug 5 and the charging jack 6 of the secondary battery pack 4.
The terminals 7 and 8 which are arranged on one end of the battery pack 4 abut upon the contact points (not shown) in the battery housing 10 of a camera 9, thus supplying the current Id discharged from the battery 11 to an exposure control circuit 12 in the camera 9.
A resistor 13 shown in FIG. 3 transforms a current flowing in the direction indicated by an arrow Ic into a voltage at the time of charging, and a current flowing in the direction indicated by an arrow Id into a voltage at the time of discharging, thus outputting it to a current detection circuit 14. The current detection circuit 14 identifies the direction of the current generated at the time of charging or discharging, and calculates the amount of current at that time of charging or discharging, thus outputting the result thereof into a calculating circuit 15. Also, to the calculating circuit 15, the output timing is applied from a timing circuit 16. In this way, the calculating circuit 15 obtains the value of the current capacitance of the battery 11 at that time by calculating the amount of current at the time of charging or discharging. The calculating circuit 15 works out the remaining capacitance of the battery 11 from the difference between the values of the current capacitance at the time of charging and that of discharging.
Here, the current detecting circuit 14, timing circuit 16, and calculating circuit 15 are fed from the battery 11 at all times through a constant voltage circuit 17. Then the value of the current capacitance thus obtained is indicated by a display means 18. Therefore, the user of the camera 9 can recognize the remaining capacitance of the battery 11 in it.
However, there are the problems given below in the secondary battery pack 4 disclosed in the Japanese Utility Model Application Laid-open No. 4-44632. As described above, the current detecting circuit 14, timing circuit 16, and calculating circuit 15 are fed at all times from the battery 11 through the constant voltage circuit 17. It is structured, therefore, that the power of the battery 11 is dissipated positively even when the battery pack 4 is left intact without being installed in the camera 9. If the battery pack is left as it is in such a state for a long time, the battery 11 is caused to discharge excessively. As well known, a nickel-cadmium battery which is used as a secondary battery is damaged most by an excessive current. Once it is damaged, the original capacity cannot be regained even if it is charged or the battery itself is destroyed, and there is a danger that it generates heat or brings about a liquid leakage when charged or discharged.
Further, in a terminating state of a battery pack 4 having a plurality of battery cells in it, there are invariably the cells among them that completely terminate the discharge earlier than others because of the individual variation of the cells. There is no problem if a charging takes place immediately even in this state, but if the battery is continuously left intact in this state, there occurs an inverted charging with respect to the above-mentioned cells by the discharged current from those cells which are yet to terminate discharging completely. It is also well known that the inverted charging produces adverse effects on a battery equally as in the excessive current. If the same process is taken when the battery is used after charging, the deterioration of the battery makes a further progress.
Not all the plural cells of a battery are given the damage described above at a time, but the damage takes place from the one cell whose condition is the worst. Therefore, even if the battery cells are packed with those having uniform characteristics, the probability of such a danger is higher for a battery pack having more cells.